Ceramic composite materials used in high temperature applications require the use of a ceramic fiber for reinforcement. Commercially available ceramic fibers are typically provided with a sizing on the fiber. Generally, any sizing is removed before coating the ceramic fiber with an interfacial coating. The resulting fiber is difficult to handle, filament wind, or weave into a 2-dimensional fabric or 3-dimensional pre-form. Additionally, an unsized fiber is prone to mechanical damage.
U.S. Pat. No. 5,093,155 issued to Miyazaki et al. on Mar. 3, 1992, discloses sizing liquid containing a sulfone compound and a solvent such as water or an organic solvent. The sizing is applied to fibers, including carbon, boron, ceramic, and metal fibers. The fibers are incorporated in a matrix resin to make a composite. The sizing enhances adhesion between the fibers and the matrix. U.S. Pat. No. 5,130,194 issued to Baker et al. on Jul. 14, 1992, discloses a coating for ceramic fibers used in composites. The fibers are generally coated with a silanol and a difunctional organic coupling agent in a water or alcohol solvent. The silanol provides hydroxyl groups on the fiber, and the coupling agent connects the hydroxyl binding sites to a resin to form a composite. However, aqueous sizing materials can damage coated fibers if the coating is moisture sensitive, resulting in deteriorated composite properties.
U.S. Pat. No. 5,173,367 issued to Liimatta et al. on Dec. 22, 1992, discloses a fiber reinforced ceramic composite. The fiber has a 2 layer size obtained by sizing the fibers with a solution of an organic solvent, a metal oxide, and a titanium compound. The fibers are then sized with an organic solvent solution of a polycarbosilane or polysilazane. The sizing protects the fibers from oxidative deterioration.
One object of the present invention is to provide a non-aqueous sizing for ceramic fibers that makes the fibers easier to handle, wind, and weave. Another object of the present invention is to provide a sizing that is easily removed by heat treatment at low temperature and leaves little or no residue when decomposed in an inert atmosphere. Another object of the present invention is to produce a sized fiber that is less prone to moisture and mechanical damage.